hcrypto.analyzer
Class CaesarAnalyzer

java.lang.Object
  hcrypto.analyzer.CryptoAnalyzer
      hcrypto.analyzer.CaesarAnalyzer

All Implemented Interfaces:

Analyzer, ExpertAnalyzer, java.lang.Runnable

public class CaesarAnalyzer
extends CryptoAnalyzer
implements ExpertAnalyzer

Assumes that the text it is passed is encrypted with a Caesar shift. It performs a brute-force Chi-square analysis to determine the likely shift.

Field Summary

Fields inherited from class hcrypto.analyzer.CryptoAnalyzer

PERMUTATION, PLAYFAIR, RAILFENCE, SIMPLESUB

Fields inherited from interface hcrypto.analyzer.Analyzer

DECIPHER_LIMIT

Constructor Summary

CaesarAnalyzer()

CaesarAnalyzer(AnalyzerFrame f)

CaesarAnalyzer(TextStatistics ts)

Method Summary

void	doAnalysis() This method performs an analysis of the text assuming a Caesar (shift) cipher was used.
void	doAnalysis(java.lang.String text)
java.lang.String	getKeywordString()
int	getOptimalShift() This method performs a Chi-Square test to find the optimal shift.
int	getOptimalShift(int firstChar, int displ) This method performs a Chi-Square test to find the optimal Caesar shift on a polyalphabetic text.
java.lang.String	getReport() Part of Analyzer interface.
void	run() Part of Analyzer and Runnable interface.
void	setup(java.lang.String text) setup() initializes the text and the result string.
java.lang.String	toString() Every class should have a toString() method.

Methods inherited from class hcrypto.analyzer.CryptoAnalyzer

prettyPrint, setup, stopThread, threadIsStopped

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

CaesarAnalyzer

public CaesarAnalyzer()

CaesarAnalyzer

public CaesarAnalyzer(AnalyzerFrame f)

CaesarAnalyzer

public CaesarAnalyzer(TextStatistics ts)
               throws java.lang.NullPointerException

Throws:

java.lang.NullPointerException

Method Detail

setup

public void setup(java.lang.String text)

Description copied from class: CryptoAnalyzer

setup() initializes the text and the result string. Note that for files containing test cryptograms, the solution is sometimes also provided following the $$$ marker.

Specified by:

setup in interface Analyzer

Overrides:

setup in class CryptoAnalyzer

run

public void run()

Description copied from class: CryptoAnalyzer

Part of Analyzer and Runnable interface. Override this method in the subclass.

Specified by:

run in interface Analyzer

Specified by:

run in interface java.lang.Runnable

Overrides:

run in class CryptoAnalyzer

getReport

public java.lang.String getReport()

Description copied from class: CryptoAnalyzer

Part of Analyzer interface.

Specified by:

getReport in interface Analyzer

Overrides:

getReport in class CryptoAnalyzer

getKeywordString

public java.lang.String getKeywordString()

Specified by:

getKeywordString in interface ExpertAnalyzer

toString

public java.lang.String toString()

Description copied from class: CryptoAnalyzer

Every class should have a toString() method.

Overrides:

toString in class CryptoAnalyzer

doAnalysis

public void doAnalysis(java.lang.String text)

Specified by:

doAnalysis in interface ExpertAnalyzer

doAnalysis

public void doAnalysis()

This method performs an analysis of the text assuming a Caesar (shift) cipher was used. The goal is to find the shift (the Caesar key). It performs a Chi-square analysis on every possible shift to find the most likely shift.

getOptimalShift

public int getOptimalShift()

This method performs a Chi-Square test to find the optimal shift. This monoalphabetic version calls the more general polyalphabetic version, which computes a chi-square test on a text beginning with the first (0th) character and proceeding through each adjacent character.

getOptimalShift

public int getOptimalShift(int firstChar,
                           int displ)

This method performs a Chi-Square test to find the optimal Caesar shift on a polyalphabetic text. It assumes that every _displ_ character starting at _firstChar_ belongs to the same alphabet. It is used primarily for analyzing Vigenere-like and Caesar-shift cryptograms.

Parameters:

firstChar - - the location of the first character in the cryptotext

displ - - the displacement (keyword length) or cycle length